1. Field of the Invention
The present invention relates to an air conditioner in which a heating load is determined in consideration of a heat loss at the outside or a room when an outdoor temperature is low and a plurality of compressors are efficiently operated depending on the obtained result of the determined heating load, and a method for controlling the air conditioner.
2. Description of the Related Art
Generally, an air conditioner is an appliance for cooling or heating a room. The air conditioner comprises a compressor, a condenser, an expansion device, an evaporator, and a refrigerant pipe. The compressor serves to compress a refrigerant into a high-temperature and high-pressure gaseous state. The condenser serves to condense the refrigerant passing through the compressor into a high-temperature and high-pressure liquid state. The expansion device serves to decompress the refrigerant passing through the condenser into a low-temperature and low-pressure liquid state. The evaporator serves to evaporate the refrigerant passing through the expansion device into a low-temperature and low-pressure gaseous state. The compressor, the condenser, the expansion device, and the evaporator are connected by the refrigerant pipe.
A heat pump-type air conditioner further comprises a direction change valve, such as a 3-way valve or a 4-way valve, adapted to change the flow direction of the refrigerant based on a cooling/heating function, thereby being selectively operated in a cooling or heating mode.
In the cooling mode of the air conditioner, an outdoor heat exchanger serves as the condenser, and an indoor heat exchanger serves as the evaporator. On the other hand, in the heating mode of the air conditioner, the outdoor heat exchanger serves as the evaporator, and the indoor heat exchanger serves as the condenser.
In the cooling mode, the air conditioner allows indoor air to pass through the indoor heat exchanger serving as the evaporator, thereby discharging cold air to the room. In the heating mode, the air conditioner allows indoor air to pass through the indoor heat exchanger serving as the condenser, thereby discharging warm air to the room.
Recent air conditioners have employed a plurality of compressors having different capacities so that the plural compressors are simultaneously or selectively operated in accordance with cooling or heating loads. Accordingly, it is possible to properly cope with the variation of the cooling or heating load, thereby optimizing the cooling or heating efficiency of the air conditioner.
In the heating mode of the air conditioner, a user sets a desirable target temperature and subsequently operates the air conditioner. Here, a heating load is determined by the difference between the target temperature and a current room temperature, and the air conditioner allows all of the plural compressors to be simultaneously operated or parts of the plural compressors to be selectively operated according to the determined heating load.
When the compressors are operated, the compressors compress a refrigerant into a high-temperature and high-pressure gaseous state. Then, the indoor heat exchanger serving as the condenser heat-exchanges the refrigerant passing through the compressors with indoor air, thereby condensing the refrigerant into a high-temperature and high-pressure liquid state and warming the indoor air. The expansion device expands the refrigerant passing through the indoor heat exchanger into a low-temperature and low-pressure liquid state. The outdoor heat exchanger serving as the evaporator heat-exchanges the refrigerant passing through the expansion device with outdoor air, thereby evaporating the refrigerant into a low-temperature and low-pressure gaseous state.
In the winter season when the outdoor temperature is low, the outdoor temperature is equal to that of the refrigerant passing through the outdoor heat exchanger or lower than that of the refrigerant passing through the outdoor heat exchanger. Accordingly, heat cannot be transferred from the outdoor air to the refrigerant of the outdoor heat exchanger. On the contrary, heat is transferred from the refrigerant of the outdoor heat exchanger to the outdoor air.
Thus, the temperature of the refrigerant of the outdoor heat exchanger is lowered by the above heat transfer from the refrigerant to the outdoor air, and the lowered refrigerant circulates through the air conditioner, thereby reducing the heating efficiency of the air conditioner.
Further, based on the load determined by the difference between the room temperature and the target temperature, all of the plural compressors are simultaneously operated or a part of the plural compressors are selectively operated. Accordingly, although the outdoor temperature is low, when it is determined that the heating load is small, only the part of the compressors are operated, thereby causing difficulty in satisfactorily maintaining the room temperature.